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Higher gross mass at the same altitude decreases the gradient and the rate of climb whereas...
  • A
    VY and VX are increased.
  • B
    VY and VX are not affected by a higher gross mass.
  • C
    VX is increased and VY is decreased.
  • D
    VY and VX are decreased.

Refer to figures.

Best Angle of climb speed (VX) is found at the maximum excess of Thrust – in other words, where the gap between the “Thrust” available and Thrust Required “Drag” curves is the greatest.

  • Weight has a very pronounced effect on aircraft performance. If weight is added to an aircraft, it must fly at a higher AOA to maintain a given altitude and speed. This increases the induced drag of the wings, as well as the parasite drag of the aircraft. Increased drag means that additional thrust is needed to overcome it, which in turn means that less reserve thrust is available for climbing.
  • This moves the Total Drag curve up, but also to the right. Thrust Required is increased and VX is a faster IAS.
Best Rate of climb speed (VY) is found at the maximum excess of Power – in other words, where the gap between the “Power” available and Power Required curves is the greatest.
  • As weight increases, the power required curve moves up and to the right. As a result, less excess Power is available and, therefore, the rate of climb decreases.
  • However, as you can see, the speed for maximum Excess Power available is higher.
Summary: higher Weight => decreased rate of climb => increased VY speed.

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